Electron beam image intensity control



March 24, 1970 w. F. BADER ET AL.

ELECTRON BEAM IMAGE I NTENSITY CONTROL Filed Nov. 12, 1968 3Sheets-Shedl 1 March 24, 1970 w. F, BADER ET AL 3,502,937

ELECTRON BEAM IMAGE INTENSITY CONTROL Filed Nov. 12, 1968 5 Sheets-Sheet2 March 24, 1970 w. F. BADER ETAI- 3,502,937

ELECTRON BEAM IMAGE INTENSITY CONTROL Filed Nov. 12, 1968 3Sheets-Sheer:l 5

Mfr of (HA/V55 f (5) United States Patent O 3,502,937 ELECTRON BEAMIMAGE INTENSITY CONTROL William F. Bader, Maplewood, and Arney Landy,Jr., Roseville, Minn., and Marvin J. Schmitz, North Hudson, Wis.,assignors to Minnesota Mining and Manufacturing Company, St. Paul,Minn., a corporation of Delaware Continuation-impart of application Ser.No. 676,860, Oct. 20, 1967. This application Nov. 12, 1968, Ser. No.774,625

Int. Cl. H01j 29/74 U.S. Cl. 315-22 10 Claims ABSTRACT OF THE DISCLOSUREThe intensity of an image produced by a pulsed electron beam beingdeflected in response to an input signal is controlled by varying theduration of the electron beam pulses in proportional response to therate of change of the input signal amplitude. The electron beam pulseduration may be accordingly varied in order to provide an approximatelyuniform image intensity.

CROSS-REFERENCE This is a continuation-in-part of our copendingapplication Ser. No. 676,860 for Electrocardiographic Recording System,led Oct. 20, 1967, now Patent No 3,434,151.

BACKGROUND OF THE INVENTION The present invention is related to meansfor controlling the intensity of an image produced by an electron beambeing deflected at a variable rate in response to an input signal.

Image intensity may be dened as the effective brilliance of the timevarying illumination sensed at a point distant from the source ofillumination within a given time interval. It is the brilliance withwhich an image appears to the human eye, to photosensitive iilm, or toother such sensing means during a given time interval within which theimage is exposed. The image intensity of a given portion of a waveformdisplayed on a cathode -ray tube is determined by the luminousintensity, the duration, and the cross-sectional area of the phosphorglow on the screen within that given waveform portion.

A problem frequently encountered in displaying Waveorms on a cathode raytube is that of the variation of the image intensity associated withvariations in the slope, i.e. the rate of change of the displayedwaveform. For example, when displaying a Waveform having as a portionthereof a relatively high slope, the slope portion appears to beconsiderably dimmer than the remainder of the waveform. In the highslope portion, the image intensity is reduced because a larger area ofphosphor must be scanned in a given time interval when there is a highrate of waveform change in contrast to a smaller area of phosphor whichis scanned in the same given time interval when there is a lower rate ofwaveform change. This problem is compounded in applications wherein thewaveform image is photographed on microlm. In some situations, the imagei11- tensity varies over such a range that proper exposure for thebrighter portion of the image display results in underexposure for theduller portions. Increasing the image intensity of the duller portion togive suicient exposure often results in overexposure of the brighterportion and may also result in burning the phosphor of the cathode raytube.

In the prior art, image intensity has been controlled by either varyingthe cross-sectional area with which the electron beam impinges theelectron sensitive medium or by varying the luminous intensity which isrelated to the energy with Iwhich the electrons impinge the electronsensitive medium.

In accordance with the prior art, cross-sectional area may be varied byvarying the electron Ibeam current density. In an image observed on acathore ray tube, the image source is within an area containing amultiple of phosphor particles. Thus, the greater the number ofparticles immediate to the image source which are illuminated, thegreater the image intensity sensed from the image source. However,illuminating a greater number of particles by increasing thecross-sectional area of the electron beam results in an image of lowerresolution. Thus, the prior art method of controlling image intensity byvarying the cross-sectional area of electron beam impingement has theinherent disadvantage of providing a Waveform of varying resolution.

Also in accordance with the prior art, image intensity may becontrolled, as stated above, by varying the luminous intensity which isrelated to the energy with which the electrons impinge the electronsensitive medium by varying the potential applied to accelerate theelectron beam or `by varying the current density of the electron beam.One disadvantage of the acceleration potential control method is thatacceleration potential variations change the deflection sensitivity ofthe electron beam. Also, such method requires high magnitudeacceleration potential variations. The current density method of varyingluminous intensity requires a focusing step to overcome the alreadydiscussed resolution problem incident to the current density method ofvarying cross-sectional area. Also as phosphor approaches its combustionpoint, its efliciency for increasing its luminous intensity in responseto an increasing impinging electron current density recreases.

SUMMARY OF THE INVENTION The present invention provides for controllingthe intensity of an image produced by a deected electron beam impingingan electron sensitive medium in pulses by varying the duration of thepulses of electron beam impingement upon the electron sensitive mediumin proportional response to the sensed rate of change of the electronbeam deilection.

Briefly, the invention comprises means which senses the rate of changeof the amplitude of the input signal to which beam deection isresponsive, and means which varies the duration of pulsed electron beamimpingements upon the electron sensitive medium in proportional responseto the magnitude of the sensed rate of change. This duration may bevaried between minimum and maximum durations in proportion to the sensedrate of change in order to maintain an approximately uniform imageintensity. The proportional relationship may ybe linear or non-linear.

In a system wherein a pulsed electron beam is deflected in response to amultiplexed plurality of input signals, the duration of each pulse issynchronized to be in response to the rate of change of the amplitude ofthe input signal deecting that pulse.

BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is a schematic diagram inblock form showing a preferred embodiment of the present inventionconnected to a cathode ray tube circuit.

FIGURE 2 is a schematic diagram in block form showing a modifiedspecific preferred embodiment of the present invention in combinationwith a circuit for time share multiplexing a plurality of input signals;

FIGURE 3 is a schematic diagram of a typical differentiator circuitwhich may be used in practicing the present invention shown in FIGURES 1and 2;

FIGURE 4 is a schematic diagram of a typical intensity modulator circuitwhich may be used in practicing the present invention shown in FIGURES land 2;

FIGURE 5 is a graphical representation of the Waveforms of the variousclocked control signals, the rate of change magnitude signal, and themodulated signal within the intensity modulator circuit of FIGURE 4 andalso of the timing signal at the critical sensing junction within thiscircuit; and

FIGURE 6 is a schematic diagram of a typical unblanking amplifiercircuit which may be used in practicing the present invention shown inFIGURES l and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the preferred embodiment, theinput voltage signal to which electron beam deflection is responsive isfed through a diferentiator circuit to obtain a signal proportional tothe slope or the rate of change of the waveform. The differentiated orrate of change signal is fed to an intensity modulator circuit whichfirst recties the rate of change signal to provide a signal of uniformpolarity. The intensity modulator circuit, which also receives signalsfrom a clock, produces a modulated signal having pulse durationsproportionally responsive to the magnitude of the rate of change. Themodulated signal is fed to an unblanking amplifier circuit which inresponse to the modulated signal applies a potential to the grid of theelectron gun to control the on-time or duration of the electron beampulses.

Referring first to FIGURE 1, a waveform is displayed on the face of acathode ray tube 10 in response to an input signal on line 12 beingsupplied through a vertical deflection amplifier circuit 14 to thevertical deflection portion of the cathode ray tube circuit 16. Thesweep signal for the waveform is supplied to the horizontal portion ofthe cathode ray tube circuit 16 from a sweep generator 18. An unblankingamplifier 20 is connected to the cathode ray tube circuit 16 to controlthe on-time or duration of the electron beam pulses by applying acontrol signal to the grid of the cathode ray tube 10 for intervalsresponsive to the modulated signal received from the intensity modulatorcircuit 22. The intensity modulator circuit 22 produces a series ofpulses at periodically clocked intervals and of varying duration inresponse to a differentiated or rate of change signal received from adifferentiator circuit 24 which indicates the time rate of change of theamplitude of the input signal on line 12. The period of the clockedintervals is in response to clocking signals from clock 26.

Retracing the operation of the electron beam image intensity controlcircuit of this invention, the input signal on line 12, which controlsthe vertical deflection of the electron beam produced image, is fed intoa differentiator circuit 24, which indicates the rate of change of theamplitude of the input signal at line 28. The rate of change signal online 28 is then fed into an intensity modulator circuit 22, which alsoreceives clocked control signals from clock 26. The intensity modulatorcircuit 22 produces a modulated signal on line 30. The modulated signalis made up of a series of periodically occurring pulses of varyingduration. The period between the beginning of each pulse is in responseto the clocked control signals from clock 26. The duration of each pulseis in response to the magnitude of the rate of change signal received online 28 from diferentiator circuit 24. The modulated signal is fed intoan unblanking amplifier 20 which produces a control signal on line 32 tothe grid of the cathode ray tube 10. The magnitude of the control signalis predetermined to be suflicient to turn on the electron gun. Theduration of the control signal is in response to the duration of thepulses of the modulated signal received on line 30. Thus, the electrongun of the cathode ray tube 10 is turned on during each periodicinterval only for a duration responsive to the rate of change of theinput signal which deflects the electron beam during that periodicinterval.

The present invention is, of course, usable with any apparatus in whichan image is produced by deflecting an electron beam and not merely witha cathode ray tube. For example, the invention could also be used withan electron beam recorder.

The present invention is especially suitable for use in combination witha circuit which provides an electron beam deflection signal in responseto a multiplexed plurality of input signals. An embodiment of such acombination is shown in FIGURE 2 and is described in some detail in ourcopending application cited above wherein a multiplex system forrecording simultaneous electrocardiographic signals is set forth.

When the electron gun responds to a multiplexedly produced deflectionsignal, it is turned on for distinct intervals for each segment of themultiplexed signal. These distinct pulses are readily controlled bymeans of an unblanking amplifier which controls the grid potential toperiodically turn the electron gun on and off to provide blank intervalsin the image during the times in which the multiplexing circuitry isbeing switched between different segments of the disparate inputsignals. The present invention provides synchronized image intcnsitycontrol for the multiplexed image producing system by controlling theon-time or duration of the electron beam pulse for each multiplexedlyproduced segment in accordance with the sensed rate of change of theamplitude of the input signal which deects the electron beam for thecorresponding segment.

In FIGURE 2, the waveform displayed on the face of cathode ray tube 10is in response to a plurality of input signals on lines 34 which aremultiplexed by signal mu1tiplexer 36, summed in summing amplifier 38with reference signals from reference multiplexer 40 to produce acomposite time division output signal on line 42 which is suppliedthrough vertical deflection amplifier circuit 14 to the verticaldeflection portion of the cathode ray tube circuit 16. The sweep signalfor the waveform is supplied to the horizontal portion of the cathoderay tube circuit 16 from a sweep generator 18. The on-time or durationof the electron beam is controlled through unblanking amplifier 20. Thesignals which control the unblanking amplifier 20 are produced in thefollowing manner. The rate of change of the amplitude of each of theplurality of input signals on lines 34 are sensed by a multichanneldifferentiator circuit 44 which produces a plurality of rate of changesignals on lines 46. The plurality of rate of change signals aremultiplexed by intensity multiplexer circuit 48 and fed to intensitymodulator circuit 22 on line 50. The intensity modulator circuit 22 alsoreceives clocked control signals from multiphase clock 52. Themultiphase clock 52 produces a plurality of disparate clocked controlsignals having a predetermined frequency but different preselectedphases. The clocked control signals are used for controlling theoperation of the signal multiplexer 36, the reference multiplexer 40,the intensity multiplexer circuit 48 and the intensity modulator circuit22 and for synchronizing their operations with each other. The intensitymodulator circuit 22 produces a modulated signal on line 30, whichsignal is made up of a series of periodically occurring pulses ofvarying duration. The period between the beginning of each pulse is inresponse to the clocking signals from multiphase clock 52. The durationof each pulse is -responsive to the magnitude of the rate of changesignal segment received on line 50 during the interval corresponding tothat particular rate of change signal segment. The modulated signal isfed on line 30 into unblanking amplifier 20. The modulated signalreceived on line 30 by the unblanking amplifier 20 determines theduration over which a control signal is fed over line 32 to the grid ofthe cathode ray tube 10 for controlling the on-time or duration of theelectron gun. The magnitude of the control signal 011 line 32 ispredetermined to be sufficient to turn on the electron gun. Thus, theelectron gun of the cathode ray tube is turned on during each intervalcorresponding to each multiplexed signal segment only for a durationresponsive to the rate of change of the amplitude of the particularinput signal which is deecting the electron beam during thatcorresponding interval.

FIGURE 3 illustrates a typical differentiator circuit which may be usedin practicing the present invention. The input signal on line 12, whichis directed to the vertical deection amplifier circuit 14 on line 54, isfed into the differentiator comprising capacitor 56 and resistor 58through an emitter follower circuit comprising NPN transistor 60| andresistor 62. The bias values of |5 .6 volts at the collector oftransistor 60 and of 5.6 volts at the open terminal of resistor 62 arethe bias values used in one typical embodiment of this invention. Otherbias values used in a compatible typical embodiment of this inventionare indicated in FIGURES 3-6 Without further comment. Identitication ofand component values for the various circuit elements shown in thecircuits of FIGURES 3', 4, and 6 are given hereinafter following thedescription of FIGURE 6. The emitter-follower circuit (60 and 62)provides a low impedance source to the diiferentiator (56 and 58) andserves to isolate the diiferentiator (56 and 58) from lines 12 and 54 sothat the input signal appearing on lines 12 and 54 will be unaffectedIby the operation of differentiator (56 and 58) Resistor 64 limits thecurrent through capacitor 56. Operational amplifier 66 maintainsjunction 68 of diferentiator (56 and 58) at near zero potential in orderto provide true differentiation. Capacitors 70' and 72 are selected topredetermine the bandwidth of frequency response of operationalamplifier 66. The output of the differentiator circuit appears on line28.

FIGURE 4 illustrates a typical intensity modulator circuit Which may beused in practicing the present invention. The differentiated signalwhich represents the rate of change of the amplitude of the input signalis fed on line 28 through an isolation circuit comprising NPN transistor74, variable impedance compensation network 76, and resistor 78 to andthrough coupling capacitor 80 to full wave rectifier 82. The variableimpedance compensation network 76 minimizes the distortion at junction84 of the signal on line 28 due to the effect of coupling capacitor 80.Isolation circuit (74,76, 78) also incidentally acts as an analoginverter reversing the polarity of the signal at collector junction 84from that received on line 28. Isolation circuit (74, 76, 78) isprovided for the purpose of isolating coupling capacitor `80 from line28 so that the differentiated or rate of change signal will be unaectedby the ope-ration of the modulator circuit of FIGURE 4. Resistors 86 and88 are biasing resistors for NPN transistor 74. Resistors 90, 92, 94,and 96 and capacitor 98 in combination with NPN transistor 99 ofvariable impedance compensation network 76 are selected to be soresponsive to frequency 'changes that the signal at the collectorjunction 84 responds at approximately the same rate as thedifferentiated or rate of change signal on line 28, although it is ofreverse polarity. Rectifier 82, comprising NPN transistors 100 and 102,PNP transistors 104 and 106, and biasing resistors 108-118, rectiiiesthe rate of change signal at emitte-r junction 120 and provides on line122 a rate of change magnitude signal representative of the magnitude ofthe dilferentiated or rate of change signal.

When a positive going signal is present at emitter junction 120,transistor 104 conducts the positive going signal to the base ,oftransistor 102 which causes transistor 102 to conduct a negative goingsignal to the base of transistor 106 which causes transistor 106 toconduct to line 122 a positive signal proportional to the magnitude ofthe signal at emitter junction 120.

When a negative going signal is present at emitter junction 120,transistor 100 conducts the negative going signal to the base oftransistor 106 which causes transistor 106 to conduct to line 122 apositive signal proportional to the magnitude of the signal at emitterjunction 120. When 6 there is no signal at emitter junction 120,transistors 106 do not conduct and no signal is conducted to line 122thereby indicating a zero rate of change of the amplitude of the inputsignal on line 12.

The rate of change magnitude signal on line 122 in combination with 30kHz. clocked control signals received on lines 124, 126, and 128, fromeither clock 26 of FIG- URE 1 or multiphase clock 52 of FIGURE 2,produces a modulated signal on line 30. Clocked signals providing resetand set control are received on lines 126 and 128 respectively.

Because of propagation delay in the reset signal on line 126, a clockingsignal is provided on line 124 to assure blanking during the intervalsbetween segments in the multiplexing operation described with referenceto FIGURE 2.

Gates 130 and 132 are connected to provide a resetset flip-Hop. Gate134, binary inverters 136, 138, and and capacitor 142 are connected toprovide a delay one-shot 143. Gates 130 and 132 deliver or maintain aPLUS pulse at their respective outputs when any one of their respectiveinput terminals receive a ZERO pulse. Gate 134 delivers or maintains aZERO pulse only when both of its input terminals receive PLUS pulses.Other circuit components include voltage dividing resistors 144 and 146,biasing resistor 148, modulation adjusting resistors and 152, diodes154, 156, and 158, NPN transistors and 162, PNP transistor 164, binaryinverter 166, and timing capacitor 168.

To explain the operation of this typical intensity modulator circuit,reference is made to FIGURE 5 which shows the waveforms of the rate ofchange magnitude signal on line 122, the clocking signal on line 124,the reset signal on line 126, the set signal on line 128, the modulatedsignal on line 30, and the timing signal at junction 170.

The amplitude of the modulated signal on line 30 is a relativelyconstant +5 volts and is representative of a PLUS control pulse. Zerovolts amplitude is representative of a ZERO pulse. The leading edge ofthe modulated signal on line 30 occurs periodically at a frequency of 30kHz. The duration of the modulated signal is dependent on the time ittakes to build up a potential at timing junction across timing capacitor168 of sufficient magnitude to overcome the positive bias provided atthe gate of transistor 164 by the rate of change magnitude signal online 122, so as to cause transistor 164 to conduct. Transistor 164 thenconducts a positive going signal to the gate of transistor 162 whichconducts a ZERO pulse to gate 132 which results in termination of thePLUS pulse on line 30.

A modulation cycle commences at time a with a new PLUS clocking pulse online 124, a PLUS reset pulse on line 126 which begins to change to aZERO pulse, and a continuing PLUS set pulse on line 128. Thiscornbination of control pulses produces either a new or a continuingZERO pulse at junction 172 as well as on line 30. A ZERO pulse atjunction 172 is led through binary inverter 166 to the base oftransistor 160 causing transistor 160 to conduct a signal having apotential slightly less than the on-bias potential of transistor 164 tothe emitter of transistor 164 thereby turning olf transistor 164, whichin turn turns olf transistor 162 which removes the ZERO pulse on line174 to gate 132.

The delay one-shot 143 produces a ZERO pulse of sufficient duration tomaintain a ZERO pulse on line 175 until after the propagation delayedreset signal on line 126 becomes a ZERO pulse, at approximately 0.5microsecond after time a.

At time b, the reset signal on line 126 becomes a PLUS pulse and the setsignal on line 128 becomes a ZERO pulse. This combination of pulsesprovides a PLUS pulse at junction 172 and on line 30. The PLUS pulse atjunction 172 is fed through binary inverter 166 to turn off transistor160 thereby enabling a potential to build up across timing capacitor168. When the potential at timing junction 170 is greater than thepotential at the base of transistor 164 (which latter potential isproportional to the rate of change magnitude signal on line 122) by anamount sutiicient to turn on transistor 164 through diode 154,transistor 164 conducts, thereby causing transistor 162 to conduct aZERO pulse on line 174 to gate 132, which results in a PLUS pulse fromgate 132.

At time c, the set signal on line 128 becomes a PLUS pulse. Thereafter,gate 130 will provide a PLUS pulse at junction 172 and line 30 only solong as gate 132 continues to deliver a ZERO pulse to gate 130. Thus,when at any time after time c there is a ZERO pulse on line 174, gate130 will cease to deliver a PLUS pulse to junction 172 and line 30. Ifthe potential at timing junction 170 has not built up sufficiently toresult in the delivery of a ZERO pulse on line 174 before the beginningof the next modulation cycle, the clocking pulse on line 124 at time awill operate to provide a ZERO pulse at junction 172 and line 30 at timea.

The interval between times b and c is selected to provide for themodulated pulse having a minimum duration of 2 to 4 microseconds in theevent the rate of change magnitude is zero, so that an image produced bya horizontally swept but nonvertically deflected electron beam will havea minimum intensity. The propagation delayed reset signal on line 126provides a ZERO pulse on line 17S before the ZERO pulse provided on line175 by the delay one-shot is completed and thereby assures blankingduring the interval a to b between segments in the multiplexingapplication described with reference to FIGURE 2.

Diode 154 protects transistor 164 from reverse bias conduction. inasmuchas the voltage drop across diode 154 and across the emitter to base oftransistor 164 is about 0.7 volt for each, two diodes 156 and 158 areconnected between transistor 160 and zero volt potential to maintain aminimum potential of 1.4 volts at timing junction 170 so that the timefor charging capacitor 168 to sufficiently initiate conduction oftransistor 164 will be proportional to the potential at the base oftransistor 164. To provide a linear proportionality, resistors 150 and152 are selected so that capacitor 168 is charged during the relativelylinear portion of its exponential charging curve. By varying theseresistors, a non-linear relationship could also be obtained wheneverdesired.

In FIGURE 5 there is shown representations of modulated signals havingvarying durations dependent upon the rate of change magnitude signal forsituations wherein the rate of change magnitude signal is (l) zero orless than 1.4 volts, (2) greater than 1.4 volts but not so great thattransistor 164 does not conduct before completion of the modulationcycle at time a, and (3) so much greater than 1.4 volts that transistor164 does not conduct prior to completion of the modulation cycle at timea.

In sequence (l), the rate of change magnitude signal is zero volts.Thus, transistor 164 conducts and causes a ZERO pulse on line 174 fromimmediately following time b. Nevertheless the potential at timingsignal junction 170 meaninglessly builds up until time c when the pulseon line 30 becomes zero due to the set signal on line 128 becoming aPLUS pulse. The duration of the modulated signal on line 30 when therate of change magnitude signal is zero volts or less than 1.4 voltslasts from time b to time c and is solely dependent on the predeterminedduration of the ZERO pulse of the set signal on line 128.

In sequence (2), the rate of change magnitude signal is quantity e,which is higher than 1.4 volts. The timing signal must reach 1.4+e voltsat junction 170 in order for transistor 164 to conduct and therebycauses a ZERO pulse on line 174. Inasmuch as the timing signal reaches apotential suicient to cause transistor 164 to conduct at time d which isafter time c, when the set signal on line 128 becomes a PLUS pulse, themodulated signal on line 30 becomes a ZERO pulse at time d. Themodulated signal PLUS pulse lasts from time b to time d and is dependenton the potential of the rate of change magnitude signal on line 122.

In sequence (3), the rate of change magnitude rises at such a rate toquantity f which is so much higher than 1.4 volts that the timing signalcannot reach a potential sufficient to cause transistor 164 to conductprior to time a when the clocking signal on line 124 causes the modulated signal on line 30 to become a ZERO pulse, which results in turningon transistor so as to return the po tential of the timing signal atjunction to 1.4 volts. The modulated signal PLUS pulse thus lasts fromtime b to time a and is responsive to the potential of the rate ofchange magnitude signal on line 122.

The interval between times b and a is selected to provide for themodulated pulse having a maximum duration of approximately 30microseconds. It is therefore seen that the duration of each electronbeam pulse is controlled to vary between prescribed minimum and maximumdurations in proportion to the rate of change of the input signalamplitude.

Referring to FIGURE 6, a typical unblanking amplifier which may be usedwith the present invention will be described. The modulated signal isreceived on line 30 and led through binary inverter 176 and lead networkcomprising capacitor 178 and resistors 180 and 182 to NPN transistor184. A positive going signal at the base of transistor 184 turns ontransistor 184 and in turn turns off NPN transistor 186 which results inthe removal of the 100 volt control signal from line 32. Line 32 isconnected to the grid of the electron gun of cathode ray tube 10. Thus,removal of the control signal from line 32 blanks cathode ray tube 10.

Therefore, a PLUS pulse modulating signal on line 30 being inverted bybinary inverter 176 to become a ZERO pulse on line 188 causes thecathode ray tube 10 to be unblanked, whereas a ZERO pulse modulationsignal on line 30 causes the cathode ray tube 10 to be blanked.

Capacitor 190 is an integrating capacitor which damps the switching ofthe binary inverter 176. Resistor 192 provides a lower input impedanceon line 188. Lead network comprising capacitor 178 and resistors 180 and182 is included to reduce the switching time of the unblanking amplifierin response to the modulated signal on line 30. Resistors 194 and 196are biasing resistors for transistor 186.

It is to be understood that the differentiator circuit, intensitymodulation circuit, and unblanking amplifier circuit described hereinWith reference to FIGURES 3, 4, and 6 are merely typical circuits oftheir particular species which may be used in practicing the presentinvention, and that various other circuits of their species may also beused in practicing the present invention by combining them in accordancewith the teachings of the present invention.

The present invention can, in fact, be practiced without the inclusionof a typical diiferentiator circuit. For example, a sample-hold methodof sensing the rate of change of input signal amplitude could beutilized. Means for separately sampling the magnitude of the inputsignal at successive measured instants and measuring the difference inmagnitudes provide `a measure of the rate of change during the measuredinterval between instants. First sampling means sense the magnitude ofthe input signal at time a and transfer the magnitude signal to holdingmeans which delay the magnitude signal to time b. At time b, secondsampling means sense the magnitude of the input signal. The signals fromthe holding means and the second sampling means are fed to adifferential amplifier which indicates the change in the input signalfrom time a to time b and thereby provides the slope or rate of changeof input signal amplitude. The interval between times a and b may be innanoseconds.

The intensity multiplexer circuit 48 may be of the same type ofmultiplexer used as signal multiplexer 36 and reference multiplexer 40as described in our hereinbefore referred to copending application andits operation is synchronized with theirs by the signals from themultiphase clock 52.

The identification of and component values for the various elementsshown in FIGURES 3, 4, and 6 are as follows:

Transistors 60-2N4124 106-2N4126 74-2N4124 160-2N4124 99-2N4124162-2N4124 100-2N4124 164-2N4126 1022N4124 184-2N3499 104-2N4126186-TRS4014LP 1 Rectifiers 154-1N9 14 156-1N914 8-1N9 14 Operationalamplifiers:

66-Motorola Model MC1430 Gates:

130-DTL946 132-DTL962 134-DTL946 Binary inverters:

136-DTL946 166-DTL946 138-DTL946 176-DTL962 140-DTL946- Resistors:

58-33KQ 114-3.6KQ 62-1KQ 116-3.6KS2 64-3.3KQ 118-10KQ 7 8-3.6\KS2144-1KS2 86-3.3KQ 14S-3.3K@ 88-2.4KS2 14S-4.7KQ 90'-47KS2 1504.7KQ92-1800 152-10KS2 94-1KQ 180-4.7KQ 96-150KQ 182-1.5KQ 10S-3.6K9 192-1KQ1103.3KQ 194-6\.8KQ 112-39KSZ 196-5K0 Capacitors:

56-.35pf. 142-470 pf. 70'-.005pf. 16S-.Olaf 72-820 pf. 17 8-100 pf.80-120,uf. 190-120 pf. 98-100,u f.

In summary, a method and system for controlling the intensity of animage produced by a pulsed electron beam being deflected in response toan input signal has been described. The diiferentiator circuit 24differentiates the input signal received on line 12 and applies a signalrepresentative of the rate of change of the input signal amplitude to anintensity modulator circuit 22 on line 28. The intensity modulatorcircuit 22 is electrically connected to and controlled by clock 26. Theintensity modulator circuit 22 is responsive to the rate of changesignal for producing a modulated signal on line 30 which is of aduration proportionally responsive to the rate of change of the inputsignal amplitude as a function of time. The modulated signal is fed online 30 to unblanking amplifier circuit which controls the duration oron-time of the electron beam in response to the duration of themodulated signal which is representative of the magnitude of the rate ofchange of input signal amplitude on line 28. Thus, the intensity of theimage can be controlled to be substantially the same for both slow andfast rise times for deflection of the electron beam.

What is claimed is:

1. A method for controlling the intensity of an image produced by apulsed electron beam being deflected in response to an input signalwherein the steps comprise sensing the rate of change of the inputsignal amplitude; and

controlling the durations of the electron beam pulses as a proportionalfunction of the sensed rate of change of the input signal amplitude.

2. The method of claim 1 wherein the electron beam pulse durations arecontrolled in response to the rate of change of the input signalamplitude for maintaining an approximately uniform image intensity.

3. The method of claim 2 wherein the electron beam pulse duration iscontrolled between minimum and maximum finite durations in proportion tothe rate of change of the input signal amplitude.

4. The method of claim 1 or 3 wherein the pulsed electron beam isdeflected in response to a multiplexed plurality of input signals, afurther step comprising synchronizing the duration of each electron beampulse to be in response to the rate of change of the amplitude of theinput signal deiiecting that pulse.

5. The method of claim 1 or 3 wherein the sensing step comprisesdifferentiating the input signal.

6. The method of claim 1 or 3 wherein the controlling step is responsiveto the sensed rate of change of input signal amplitude through a stepcomprising producing a modulated signal in response to the sensed rateof change of the input signal amplitude.

7. A circuit for controlling the intensity of an image produced by apulse delectron beam deflected in response to an input signal,comprising means for sensing the rate of change of the input signalamplitude; and

means operatively coupled to the sensing means for controlling thedurations of the electron 'beam pulses as a proportional function of thesensed rate of change of the input signal amplitude.

8. The circuit of claim 7 wherein the pulsed electron beam is deflectedin response to a multiplexed plurality of input signals, furthercomprising means operatively coupled to the sensing means and to thecontrol means for synchronizing the duration of each electron beam pulseto be in response to the rate of change of the amplitude of the inputsignal deflecting that pulse.

9. The circuit of claim 7 wherein the control means controls theelectron beam pulse durations to maintain an approximately uniform imageintensity.

10. The circuit of claim 7 or 9 wherein the control means is operativelycoupled to the sensing means through a modulating means which provides amodulated signal to the control means in response to the sensed rate ofchange of the input signal amplitude.

References Cited UNITED STATES PATENTS 2,700,741 1/ 1955 Brown et al.315-22 2,993,142 7/ 1961 Harvey 315-22 3,130,346 4/ 1964 Callick 315--22RICHARD A. FARLEY, Primary Examiner T. H. TUBBESING, Assistant ExaminerU.S. Cl. X.R. 315--30

